This invention relates to a method and device for eliminating the effect of periodic disturbance variables having a known, variable frequency in general and more particularly, to a method and device for eliminating the effect of periodic disturbance variables having a known, variable frequency affecting control loops between the controlled system and the final controlling element.
These types of frequency-variable disturbances originate in the case of driving mechanisms, for example, from torque ripple factors proportional to rotational speed and result from design-dependent flux asymmetries in the machine, or periodic bearing load content caused by a rotating out-of-balance force in electromagnetically supported rotors.
German Patent 26 58 692 discloses compensating for the effect of such an out-of-balance force, in the case of a magnetic rotor bearing arrangement, by means of a control loop in a transformed coordinate system, which is fixed relative to the rotor. With this method the effect of the out-of-balance force in the effective circuit across the controlled system is eliminated by the controller. This means that the changes in position produced by the periodic out-of-balance force must first pass through the closed loop before they can be eliminated by the position controller. Only moderately fast frequency variations in the disturbance variable can be effectively dealt with using this method.
In view of the prior art, there is a need for a method and device to eliminate disturbance variables occurring in control loops with a wider range of frequency variation.